The present invention relates generally to rotary transformer circuits in magnetic recording and/or reproducing apparatuses having rotary magnetic heads. More particularly, the invention relates to a multiple-channel transformer which is provided with coils in correspondence with rotary magnetic heads of a plurality of channels, and in which the interval between the coils is made small, and, moreover, signals can be obtained without cross-talk from other channels.
Heretofore, a so-called two-head type, helical-scanning magnetic recording and/or reproducing apparatus, in which video signals are recorded and reproduced alternately by a pair of rotary magnetic heads on and from a magnetic tape along tracks that are obliquely orientated relative to the longitudinal direction of the magnetic tape, have been widely reduced to practice. In a magnetic recording/reproducing apparatus of this two-head type, however, there is a need for an organization of means by which, with respect to tapes of the same length, recording and reproducing can be carried out with different modes of recording/reproducing time such as, for example, 2 hours and 6 hours.
In this case, for the 2-hour recording and reproducing mode, the magnetic tape is driven at a travel speed for 2 hours, and recording and reproducing are carried out with a pair of magnetic heads for 2-hour use. On the other hand, in the case where the apparatus is set for the 6-hour mode for long-time recording or reproducing, the magnetic tape is driven at a slow speed for 6 hours, and recording or reproducing is accomplished with a pair of magnetic heads for 6-hour use of narrower track width than that of the heads for 2-hour use. For this reason, in a magnetic recording/reproducing apparatus in which the recording or reproducing time can be changed in the above described manner, a pair of rotary magnetic heads for 2-hour use and another for 6-hour use, or a total of two pairs of rotary magnetic heads are used.
Furthermore, in the case when changed-speed reproduction of a signal at a specific speed which is different from that at the recording of that signal (for example, double speed quick motion or one half speed slow motion) is required, a pair of rotary magnetic heads exclusively for changed-speed reproduction mounted at different height positions are provided in addition to the pair of recording and/or reproducing rotary magnetic heads.
A magnetic recording/reproducing apparatus wherein a plurality of pairs of rotary magnetic heads are provided on a rotary structure, and, of these, only one pair of rotary magnetic heads are changed over and used according to a selected mode is being developed and reduced to practice.
On one hand, in a magnetic recording/reproducing apparatus in which rotary magnetic heads are used, in general, a rotary transformer is used for the transfer of signals between the rotary magnetic heads and the electrical circuit on the stationary side. This rotary transformer is mounted on the rotary structure on which the rotary magnetic heads are mounted and comprises a rotor comprising a disc-shaped core and coils formed thereon in a concentric circular arrangement and connected to the rotary magnetic heads, and a stator comprising a disc-shaped core and coils formed thereon in a concentric circular arrangement so as to confront the coils of the rotor.
A rotary transformer in a magnetic recording/reproducing apparatus of the type in which, of the above mentioned plurality of magnetic heads, one pair of magnetic heads is selectively used is of a multiple-channel organization in which coils are disposed in correspondence with the magnetic heads (four coils being used in the case where two pairs of magnetic heads are employed). The circuit of a multiple-channel rotary transformer of this kind has a circuit organization wherein the coils are provided in parallel connection, and, between each coil and an amplifier, an ON-OFF switch is individually provided therefor and is connected thereto. In accordance with the recording/reproducing mode, the switch corresponding to the pair of magnetic heads to be used is closed, and the switches corresponding to the pairs of magnetic heads not used are opened to open the circuit.
If a multiple-channel rotary transformer were to be constructed to have an increased number of coils with a conventional circuit organization as it is, the resulting structure would be disadvantagiously large. Particularly in a magnetic recording and reproducing apparatus for home use, the diameter of the rotary drum on which the rotary magnetic heads are mounted is standardized at a relatively small value, and it is difficult to use a large multiple-channel rotary transformer. Accordingly, a possible solution to this problem would appear to be to make the diameter of the disc of the rotary transformer small in order to install it within a guide drum of this small size and to reduce the interval between the coils disposed in a concentric circle.
However, if the interval between the coils is made small with the above mentioned circuit connection arrangement as it is, at the time of reproduction, for example, cross-talk will be disadvantageously produced to a degree which is not negligible from the coils of the channels of the pairs of magnetic heads not in use to the coils of the channel of the pair of magnetic heads in use.